Shakers or other vibrating devices can be used to separate solids from fluids. Some shakers have multiple screen assemblies having screens with a porous material for separating the solids from the fluid. The fluid passes through the porous material and the solids remain atop the screen to be conveyed off. The screen assemblies can have a stepped arrangement. Solids fall from the discharge end of each screen assembly to the feed end of the next screen assembly. With some solid materials, conveyance along the screens can be hindered because the particles get caught in the screen resulting in a pileup of solids and blinding of the screen surface. As used in this application, “blinding” refers to the condition when a screen has lost much of its filtering capability due to the pores within the screen being plugged to the point of substantially interfering with fluid flow through the screen. When significant blinding occurs, the separation process must often be temporarily stopped to clean the screen. If particles are not removed from the pores, then the life of the screen can be significantly shortened due to screen blinding.
One industrial process that requires effective separation of fluids from solids is in industrial metal manufacturing. In the process to produce rolled steel, an ingot of molten metal is poured through brass openings that are typically 5 or 6 ft long and about 6 inches wide in the narrow direction. These brass openings are cooled with water on their back side. A rectangular billet is formed and then it is cut to length and the rolling process begins. Water is sprayed on both sides of the surface of the billet as it is rolled narrower and narrower. As the steel is exposed to the air, mill scale develops on the surface of the steel. Mill scale is a metal oxide that forms due to the reaction of the oxygen in the air with the metal surface of the steel.
During the rolling process the mill scale must be removed from the steel. In most steel mills, high-pressure water is used to remove the mill scale. In some processes, the spray nozzles spray water at pressures up to 7,000 psi on the surface of the steel. Other rolling processes use water pressures about 4,000 psi. Lower pressure water sprays tend to leave more mill scale on the surface of the steel. The mill scale is blasted off the surface of the steel again and again as the sheet of steel is rolled to the correct thickness. The steel is then cut again to length and coiled while it is still red hot into a coil. The mixed stream comprising mill scale and water is often referred to as “mill slag”.
Some processes can use fresh water in the high pressure spray. However, most processes use recirculated water recovered from the mill scale removal operation. Therefore, it is important that the mill remove as much particulate matter from the recirculated water. The presence of mill scale particles can shorten the life of the high pressure pumps and spray nozzles used due to erosive wear. In addition, mill scale particles in the recirculated water can contaminate the processed steel. If a spray nozzle becomes plugged it may result in the steel sheet being “out of spec.”. The price for this sheet is often reduced.
Mill scale is steel oxide which is in the form of thin plate-type particles after it is blasted off the surface of the steel. Vibratory screen devices are not commonly used in operations involving mill scale removal because these plate-type particles tend to plug and blind a screen. One possible mechanism for this plugging is that the plate-type particles tend to get caught in the square or rectangular openings, much like fibrous materials but more so because of the shape of the particles. Changing the shape of the openings in the screen can reduce the propensity of the mill scale particles to hang up and plug the openings of screen; rounded openings such as circular or oval openings are examples of such openings.
To increase the operating life of the screen, fluid can be sprayed onto the screen to remove any mill scale particles that have built up on the surface of the screen or are trapped within the screen openings. The spray can be directed from underneath the screen in a reverse-cleaning process. The spray from underneath the screen further de-blinds the screen of the small amount of solids which are a similar size and shape as the hole openings. In some embodiments the spray can be directed from above the screen to remove the particulate from the surface and aid in its conveyance to a sequential screen assembly.
There is a need for a process to separate mill scale from fluid that provides consistent and effective conveyance of the mill scale during the separation and for a screen that can be used to improve this process.
The instant invention, with its multiple embodiments as disclosed within this application, provides a process and a screen that fills this need. The art referred to and/or described within this application is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a thorough search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention, a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well, only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.